1. Field of the Invention
The present invention relates to an internal combustion engine of the direction injection type and more specifically to a Saurer type direct injection Diesel engine which features a unique cavity and fuel injector arrangement.
2. Description of the Prior Art
In Saurer type engines (see FIG. 1) a problem is encountered in that it is difficult to simultaneously use large diameter inlet and exhaust valve and dispose the fuel injector nozzle coaxially with the cylinder bore axis. Accordingly, various attempts have been made to offset the fuel injector and modify the location of the toroidal cavity into which the fuel is injected in an effort to relieve the crowding problem while providing desirable performance characteristics. However, until now none of these efforts have proved satisfactory.
Japanese Patent Application Second Provisional Publication No. 56-7494 (shown in FIGS. 2 and 3 of the drawings) discloses one example of the above mentioned proposals. This arrangement includes a cylinder bore 1 (having an axis O.sub.1) a piston 2 reciprocatively disposed therein, a toroidal cavity 3 formed in the crown of the piston, a cylinder head 4 which closes the cylinder bore 1 to define a variable volume combustion chamber and a fuel injector 5 disposed in the cylinder head 4 and arranged to inject fuel into the cavity 3. In this arrangement the fuel injector 5 is of the type having a nozzle formed with four injection apertures or ports each arranged at 90 degree intervals. As shown in FIG. 1, the injector is arranged so that the nozzle thereof is coaxial with the axis of rotation of the toroidal cavity. Viz., the axes O.sub.2 and O.sub.3 of the injector and the cavity are aligned.
FIGS. 4 to 6 show the evolution of the just described arrangement from what shall be termed an "O" type arrangement (see FIG. 1 for example) wherein the centre of the fuel injection nozzle O.sub.2, axis of rotation of the toroidal cavity O.sub.3 and the axis of cylinder bore O.sub.1 are all aligned.
FIG. 4 shows what shall be referred to as an "A" type arrangement. In this arrangement the cavity 3 is formed in middle of the piston crown so that the axis of rotation thereof is coincident with the cylinder bore axis O.sub.1 and the centre of the fuel injector nozzle O.sub.2 offset as shown. This arrangement while being simple has suffered from the drawback that the fuel injected along trajectories T.sub.1 and T.sub.2 has insufficient time to atomize and tends to wet the walls of the cavity 3. To overcome this it was subsequently proposed as shown in FIG. 5 (viz., type B) to offset the cavity so that the axis of rotation of the cavity O.sub.3 and the center of the injection nozzle O.sub.2 were coincident and thus equalize the lengths of the trajectories followed by the fuel. However, with this modification (i.e. type B) a problem was encountered in that the flow patterns within the cavity due to squish and reverse squish effects are not symmetrical as required.
To overcome this problem it was subsequently proposed as shown in FIG. 6 (viz., type C) to add a lip 6 which corrected the asymmetrical flow patterns. As will be understood this "C" type arrangement of FIG. 6 corresponds to that shown in FIGS. 2 and 3.
Experiments conducted with the above mentioned "O", "A", "B" and "C" type engines revealed that:
When the offset of the axis of rotation of the cavity O.sub.3 relative to the cylinder bore diameter is approximately 6% or less, the performance of the engine differs very little from that of the "O" type.
When the offset of the fuel injector nozzle center O.sub.2 from the axis of rotation of the cavity O.sub.3 with respect to the diameter of the cavity (referred to as "first nozzle excentricity" hereinafter) is 10-12% or less the power output performance of the engine is scarcely effected.
In general a compromise may be struck between maximizing fuel flight trajectory length and squish/reverse squish strength by setting the cavity diameter approximately 50% of the cylinder bore diameter and the first nozzle excentricity at 5-6%.
With the "A" type engine when the offset of the fuel injector nozzle O.sub.2 from the cylinder bore axis O.sub.1 with respect to the diameter of the cylinder bore (referred to as "second nozzle eccentricity" hereinafter) is 6% or less the power output deviates very little from that of the "O" type engine, as shown in FIG. 10. Under the same conditions, the "B" type engine exhibits the same performance characteristics. The provision of the lip in the "C" type engine improves the output a little, as shown.
In the case that the second nozzle excentricity is more than 6% and the cavity offset in a manner that the axis of rotation O.sub.3 thereof is aligned with the center of the injector nozzle O.sub.2 such as shown in FIG. 7 (viz., "D" type) the output performance of the engine falls off markedly. However, with the provision of squish/reverse squish correcting lip 6 ("E" type) shown in FIG. 8 the performance of the engine is notably improved.
If the offset of the cavity is less than that of the fuel injector nozzle, wherein the first nozzle excentricity is 12% or less and the cavity is offset by 6% of the bore diameter (see "F" type in FIG. 9) the performance is slightly deteriorated as compared with the "E" type.
Thus, in summary, even if the second nozzle excentricity exceeds 6% a sharp deterioration in performance characteristics can be prevented by employing "E" of "F" type arrangements, but it is impossible to obtain any notable improvement over the basic "O" type. This is especially so when the second nozzle excentricity exceeds 11-12% in the "E" and "F" type arrangements.
Further disclosure regarding the above mentioned "E" and "F" type arrangements may be had with reference to FIGS. 4 and 2 respectively, of Japanese Utility Model First Provisional Publication No. 57-36324.